This invention relates to a fluid pressure regulator.
In an air assisted ink jet head, such as described in U.S. Pat. No. 4,613,875 issued Sept. 23, 1986, air is delivered under pressure to the ink jet head and forms a stream of air which assists in detaching ink droplets from an aperture plate in the ink jet head. In order to provide consistent copy quality, it is necessary that the pressure with which air is supplied to the ink jet head be regulated. If more that one type of print receiving medium is used, e.g. not only paper but also transparent film, it may be necessary for optimal operation of the ink jet head, to employ regulated pressures of different magnitudes with the media respectively.
The Tektronix 4692 color copier employs air assisted ink jet heads and has a pressure regulator that comprises a housing defining a cylindrical chamber. The housing also defines an inlet opening for introducing fluid under pressure into the chamber, and an outlet opening for allowing air to leave the chamber at a regulated pressure. The housing further defines two bleed orifices which are spaced apart from each other and from the outlet opening in a direction along the central axis of the cylindrical chamber. The bleed orifice that is axially closer to the outlet opening is provided with a valve, whereby this orifice can be opened or closed selectively. A piston is fitted in the chamber and is movable between a first position in which both bleed orifices are in open communication with the inlet and outlet openings and a second position in which the bleed orifices are effectively isolated from the inlet and outlet openings. A spring biases the piston towards the second position. When air under pressure is supplied to the outlet opening and the valve is open, the piston tends to an equilibrium position in which it partially closes the first bleed orifice. Similarly, when the valve is closed, the piston tends to an equilibrium position in which it partially closes the second bleed orifice. The difference between pressure that exists in the chamber when the valve is open and that which exists when the valve is closed is a function of the area of the piston, the spring constant and the axial distance between the bleed orifices.